I still haven't had the time to replace the MC and PV... Or put the speed bleeders on. But, I did finish putting the new cover and seat belts on the rear seat! Small accomplishment.... But, a step in the right direction.

That valve does a number of things, but the one you need to be concerned with right now is shutting off flow to a 'Leak'.
When pressure drops on one end of the vehicle, a spool valve moves to close off that leak so you still have brakes on one end.

You have TWO choices.
One is to bleed the front to relieve the line pressure so the valve can move back to center.
Once you have done that, you can switch between front and back to keep that valve centered as you bleed.

The second option is to buy a little spring clip that holds the valve centered while you are bleeding.

Keep in mind, if you bleed the front and the valve still doesn't center,
You may need to take it apart and clean it.
Years of rust, moisture, dirt accumulate in the valve, and stick the spool valve in it's bore, making it impossible to bleed one end while holding pressure on the other.

I've had to run back and forth before to get them bled, but one trick is to start in the back first,
Bleed the rear, then the front. I know that's backwards to what a lot of people say, but it works.

I've also left a front bleeder cracked a little so the front can 'Drain' while the rear gets bled. You have to keep a close eye on the master cylinder with you do that, but it does work.

There will be a line going into one 'End' of the combo/safety valve, and on the other end there will be a rubber cap that covers the end of the spool valve stem.
Seeing if that valve stem moves while you are pumping the brakes will usually tell you if the spool valve is stuck in the bore or not,
If it's moving, you need to hold it centered while you are bleeding.

Once you get pressure to both ends, the valve will stay centered, problem solved...

JeepHammer,
Thanks for your post! Now, I understand a little more about how that PV works & it actually makes sense! The new PV was spraying fluid from around the pin, so I ordered another one... It's here now, but I'm not sure how I'm going to install it yet. I got a SSBC adjustable PV, but looking at the directions and parts included- I am going to have to change the thread size on the brake lines.
I guess I could use a dremel to cut the lines, but I don't know the first thing about flaring lines.
I'm really close to hiring someone to finish this job for me!

The process of making my bottle openers..
I started with a 2'x2' piece of scrap diamond plate! Made a cardboard template, traced them out, use the metal shop at work to cut & sand to size... Took them home & finished the job.

Flaring brake lines is easy. All you need is a mini tubing cutter and a flaring tool. It would help if you post a picture of the parts you received with your PV kit. You may be able to buy adapters to convert from one thread to another. Do I recall that you replaced the PV with an OEM one sometime back. I had a 71 Vette do the exact same thing, the PV was stuck and no fluid to the rear brakes. A stock replacement PV and I was good to go. I don't think you need an adjustible PV until you add rear discs.

The combo valve is a pain in the butt sometimes,
When the spool moves off center, it turns the 'BRAKE' light on in your interment cluster.

It buffers the front discs so they aren't locked up by the time your rear drums start grabbing some... If the back brakes grab first, you brake in a straight line,
If the front brakes grab and lock first, you don't have steering.
It turns on the warning light on the dash.

Keeping it centered is as easy as letting the front end bleed openly while you bleed the back since there won't be a pressure differential with both open.

I've had to run between front and back (Once each, then repeat) a million times to get stubborn systems to bleed.

Now, a 'Proportioning' valve is nothing more than a valve you limit the amount of fluid that can get through to one end or the other.

Normally, you put a proportioning valve in the line that feeds the back end so you can reduce pressure to the back.
Since weight shifts FORWARD when you try and stop, you want most of your breaking power in the front, so with the race cars, we all but cut off the back brakes during braking tests. The rears are only going to get lite and lock up anyway...

SSBC should have a tool for keeping that valve they are selling centered, and you have had to return defective merchandise, so twist their 'Arm' for that centering tool! If it were my company, I'd send that little clip to you just to sooth a customer's nerves...

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Flaring brake lines isn't a huge issue, but it MUST be done correctly.
Double flairs in most cases with these older Jeeps, but I don't know what SSBC uses, there might be some bubble fittings...

We covered flaring brake lines at the first Jeep Clinic because this is something that DOES pop up from time to time.
You will need a specialized tool called a 'Double Flaring' or 'Inverted Flair' tool.
Most brake lines are double flared to make the connections stronger, and it's not rocket science, but it does take some skill.

Wish you lived closer to me, I would teach you how to do this...
Maybe this would be a good 'Write Up' for the forum?
Anyone else wish they knew how to do brake flairs?

It looks fairly straight forward. All you need is a flaring tool and a mini tubing cutter. The issue will be, and it always happens to me, is that you will undoubtedly break a brake line when you start yanking, pulling and bending them. The other issue is if you cut the fittings off you may not have enough left. Be forewarned that Advance Auto Parts brake line is NOT the same quality as factory. They will rot in 3 years, so if you have to add line you will need to keep your eyes on it in the future. That's why my Jeeps have Stainless Steel brake lines if anything needs replacing. Do it once!

I think I'll start from scratch on the brake lines... Before I even start changing parts I'm ordering all new SS brake lines. And, I think I'll leave the flaring to someone that's experienced. There are 2 places in town that I'm sure can handle the task.
In the meantime, I plan to spend the weekend on my new pontoon... Floating in the middle of the lake somewhere! Thanks to all of you for all of the advice!!!! I'll post an update after the brake lines are ready & I get back to working on her!